In the automotive industry, many parts for the vehicles are manufactured using a moulding process. The moulding process is particularly well suited for high volume production of parts.
In particular, injection moulding has been used extensively to manufacture various parts. A mould is manufactured in at least two parts such that when put together, a cavity is formed which is filled with a molten plastic or metal material which hardens to the desired shape and size of a finished product.
In order to reduce the size and weight of many moulded parts, the part is designed to have a relatively thin shell. However, in order for the part to be attached in the desired location, special attachments must be provided to receive screws to fasten the part at the desired location. A boss is normally moulded directly to the part from which connectors can be moulded to receive screws for fastening the part to the desired location.
It is a well-known rule in the art of moulding that the thickness of an attachment on the rear face of a part cannot exceed 60% of the thickness of the shell to which the attachment is moulded. If the thickness of the boss exceeds 60%, a "sink hole" will be formed on the outer shell of the moulded part. The sink hole results from the shell cooling and shrinking at a different rate than where the boss attaches thereto. The presence of a sink hole in the finished part is highly undesirable and can result in rejection of the part by the manufacturer and the consumer.
The different rates of cooling of the solid boss and the thinner shell portion cause a further problem. If a high rate of production is used, the moulded part is removed from the mould when the solid boss portion is still hardening. Unless the part is maintained in a position where the connecting tube extends vertically, the connecting tube will have a tendency to sag as the boss hardens. This process will cause the connecting tube to become misaligned resulting in a high rate of rejection during assembly of the part.